Photodiode arrays are designed specifically for registration of fast optical signals with typical duration time from several picoseconds to a microsecond. Such photodiode arrays usually have one common electrode for a common working voltage supply to every element of the array. In addition, each element of the array typically includes another independent electrode to read out its individual electric signal. This configuration provides very fast read-out of the signal from all of the photodiodes of the array.
Presently, photodiode arrays are widely used in research equipment and in consumer electronics as position-sensitive light detectors. However, a number of applications, such as Cherenkov detectors, medical tomography and others require relatively large photodiode arrays, with minimised dead (insensitive) space both between elements (photodiodes) of the array and along the array perimeter. A problem associated with the manufacturing of photodiode arrays is that as the number of elements increases, it becomes increasingly difficult to have a contact from the elements in the centre of the array. Traditionally, this problem is solved by tracing several conductive strips between the sensitive areas, but this leads to reduction of the sensitive area of the photodiode array.
One of the approaches known in the art (disclosed in U.S. Pat. No. 7,714,292 incorporated herein by reference) is based on an epitaxial semiconductor layer grown on top of a dielectric substrate. Contacts of the array elements are routed to the back surface of the epitaxial layer (that is to the boundary between the substrate and the epitaxial layer), and then taken along this boundary to the perimeter of the array. Deep doping of the back side of the epitaxial layer is used for electric insulation of the photo elements from each other. This approach requires an extremely complicated technology of epitaxial layer transfer from one substrate to another. Accordingly, the main drawback of this approach is its high cost as a consequence of very complicated fabrication technology.
Another technology known in the art (disclosed in U.S. Pat. No. 6,853,046 incorporated herein by reference) comprises a semiconductor substrate formed with an array of photodiodes on the light incident surface side. Here, the semiconductor substrate is used as common electrode for the array. A through hole penetrating through the semiconductor substrate from the light incident side to the opposite surface side is formed in an area held between photodiodes of the array. An individual conductive layer extending from every photodiode on the light incident side to the opposite surface side by way of a wall surface of the through hole is formed perpendicular to the light incident side. The conductive layer going to backside of the semiconductor substrate are used as individual electrodes the array photodiodes. The need for an insulated through hole between the sensitive elements leads to an increased dead space between them, constituting one of demerits of this approach.
Another photodiode array is known in the art (disclosed in N. Dinu et al. Characteristics of a prototype matrix of Silicon PhotoMultipliers (SiPM)—JINST, 4, P03016, (2009) incorporated herein by reference). In this approach, photodiodes of the arrayed photo-detector are disposed on a common semiconductor substrate, which also acts as the common electrode of the array. The individual electrodes of each photodiode are routed out to the perimeter of the array along the surface of the semiconductor substrate. In order to do that, special conductive strips insulated from both the substrate and photodiodes of the array are formed on the face side of the semiconductor substrate. One end of the conductive stripe is connected to a photodiode of the array and the other one to a metal pin located at the perimeter of the array. The conducting strips are disposed between the photodiodes, thereby leading to reduction of the active surface of the photodiode array. As the number of photodiodes in the array increases, the gap between them has to widen as well to accommodate a larger number of conductive strips. This leads to a dramatic increase of dead space of the photodiodes array, being a fundamental drawback of the said device.
Although some progress has made with respect to the development and manufacture of semiconductor photodetector arrays including avalanche photodiodes arrays, there is still a need in the art for new and different types of photodetector arrays. The present invention fulfills these needs and provides for further related advantages.